The invention relates to a method for the treatment of waste products, in particular waste products of reactive metals which are contaminated with oil and oleaginous cooling agents, and to an apparatus for carrying out such method.
When metals are machined, a number of waste products are automatically produced in the form of particles or chips, e.g. fillings turnings, borings or machining chips. In the machining of reactive metals, for example magnesium and magnesium alloys, oil or oil containing cooling fluids are employed. The machined chips will therefore be contaminated with oil. This constitutes a serious environmental problem for the users since there is virtually no commercial utilization for oil-contaminated chips today. It is costly for the users to deposit the waste. For this reason it would be desirable for as much as possible of this waste product to be recovered, but the oil in conjunction with highly inflammable magnesium chips presents problems. Remelting of the oil-contaminated chips has been attempted, but this method is not recommended as such chips burn and, to a certain extent, also cause magnesium melting loss. The oil must therefore be removed before any remelting is undertaken.
A usual recovery process which can be used for brass or aluminum chips is centrifuging and/or washing of the chips with a subsequent drying process. Such a process is described in U.S. Pat. No. 4,721,457. Concerning more reactive metals, such as magnesium and magnesium alloys, this method is not suitable. The magnesium reacts with water, releasing hydrogen, which is hazardous. Furthermore, the surface of the chip will be oxidized so that the product will become even less suitable for recovery than it was at the start. The oil content in the washed product will also be relatively high, approximately 0.5-1%.
The use of solvents will remove the oil from the oil-coated chips quite well. However, this is an expensive method and not very acceptable from an environmental point of view.
Previously there have also been methods based on thermal removal of oil. German published application No. 2 522 659 sets out a method of recovering grinding chips from nickel and chromium alloyed steel. The chips, which can contain up to 20% oil, are first centrifuged. Thereafter the oil is vaporized by means of induction heating and is recovered by distillation.
Magnesium chips are a material which has to be handled with great care due to its pyrophoric characteristics. Magnesium is inflammable in the presence of oxygen, and increasing temperatures also increase the vapour pressure. In ordinary use the heating of magnesium to above 200.degree. C. is considered hazardous.